Overshoot effect and inflexion characteristics in transient electroluminescence of hybrid phosphorescent OLEDs

The electroluminescence (EL) transient responses of Ir(ppy)₃:CBP-based hybrid organic light emitting diodes (OLEDs) have been investigated. An inflexion point phenomenon of the EL fall time (t_f) response in phosphorescent OLEDs with a hole blocking layer (HBL) was found. It can be attributed to the quantity variation of accumulated carriers at internal interfaces. The overshoot effect in transient EL is also analyzed. The phenomenon that the EL overshoot time (t_s) extended as the pulsed voltage increased is found for the first time. It is deduced that this phenomenon is related with triplet excitons’ long lifetime. It is also demonstrated that the delay time (t_d) response is mainly influenced by the hole injection barrier of OLEDs. (paper)